1. Field of the Invention
This invention relates generally to breathing ventilators, and more particularly concerns a spring piloted safety valve for a lung ventilator that provides ventilation pressure relief when ventilation pressure exceeds a maximum pressure limit, and that provides an emergency path through the safety valve to allow the patient to breathe in the event the ventilator become inoperative for some reason.
2. Description of Related Art
Medical ventilators are generally designed to ventilate a patient's lungs with breathing gas to assist a patient in breathing when the patient is somehow unable to adequately breath without assistance. For inspiration, common ventilators use positive pressure to initiate gas flow into the lungs, while exhalation occurs passively. Typically, inspiratory pressure is controlled through a closed loop inspiratory valve control. To prevent gas from escaping and to provide primary over pressure protection, an exhalation valve is set to a preselected maximum ventilation pressure.
In the event that a system failure occurs, a secondary pressure relief valve is commonly used to limit potentially damaging pressure in the lungs. Pressure relief valves used in this matter are commonly known as safety valves. Most safety valves are set to provide pressure relief at a fixed pressure which is higher than the maximum ventilation pressure, yet low enough to meet maximum pressure limits as set by regulatory agencies.
A feature common to safety valves is that they are pneumatically normally open. In the event of power loss, this gives a spontaneously breathing patient the ability to draw ambient air in through the safety valve.
One known ventilator system includes a safety valve comprising a pivotal plate with an adjustable sealing poppet that fits over the valve opening. Springs are connected to the plate to pull the sealing poppet to cover the valve opening. A spring loaded piston is biased against an end of the plate by a spring to exert a torque pivoting the plate to open the safety valve. An electromagnet pulls the piston against the force of the spring loading to allow the valve to close, and when power to the safety valve is interrupted, the valve is allowed to open. The safety valve opens when excessive pressure accumulates in the inspiration section, at a preprogrammed overpressure, and acts as an emergency valve, opening in the event of a power failure, to provide the patient with air through the open safety valve. However, the air path to the patient in the event of power failure with such a system is relatively restricted.
In the event of ventilator over pressure conditions, it would be desirable to provide a pneumatic system for further opening the safety valve, to thereby more rapidly reduce excess patient pressure, thus lowering the risk of barotrauma. It would also be desirable to provide additional safety by reducing patient pressure as flow increases, to have the ability to tune the valve's pressure relief response time, and to dampen oscillations. The present invention meets these needs.